Sega Turbo - Cars, buildings and trees really tall - FIXED

gamefixer

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Sega Turbo - Cars, buildings and trees really tall - FIXED

Just thought I'd post this for future searches.

Got a Turbo PCB on the bench this afternoon. Cars, trees and buildings were all really tall. The two adjustment pots on the PROM board made very little change to the size.

Verified that +/- 12 were at the board, pulled and tested the TL084's and the 4016s, all good.

On a whim I though, may as well replace the LS373 at IC1. Got lucky, that was it!
 

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Going to add a bit extra to Gamefixers useful post for future searchers too. A failed UPC624 @ IC5 can cause the exact same visual problem. The reason why is quite interesting (or at least I thought so :p). The sprite scaling in this game works by using an 'analog' clock signal to the sprite eproms when putting out the scanline. When a 'scaled' sprite is drawn the clock is slowed down compared to the scanline clock, so the sprite stretches longer across the scanline (remember it's a vertical monitor game, so a sprite stretching up the screen is really stretching across the scanline).

What goes into the LS373 is the x-scale for whatever sprite is highest priority on that scanline. That output then goes to the DAC (UPC624) which drives some other analog bits before going back to digital. So if your LS373 has stuck high outputs you'll get maximum stretched cars, but also if the DAC is failed and outputting max analog voltage you'll get the same thing. If the later bits of the analog section has failed you probably won't see any sprites at all as the sprite clock will be dead.

At least, that's how I _think_ it works. :)
 
NICE! There is so little information about this game. The more that gets added to the database the better.
 
Thanks for posting guys. Great stuff!

I'll be working on a few Turbo board sets pretty soon, so I keep an eye out for any and all info. Adding this to the list.
 
I would like to add to this, since this thread assisted me, that I fixed this issue on my board by replacing UPC624 @ IC5. Mine was a UPC624C, which I replaced with a UPC624D - both are available online but I ordered the wrong one and it was a few bucks cheaper. Oops. :) Appears to not matter and that some of these boards may have come stock with UPC624D anyways, and it's even the variant listed in the official schematic despite my board being factory populated with "C". It appears the guy below replaced his "D" with "C", so it works vice versa too. ;)

I did also replace the LS373 at IC1 first but, unlike gamefixer's personal board, it was not the problem on mine and thus had no effect. It's about a 50/50 chance, although I'd probably recommend anybody start with the UPC624 first.

My sprites actually "bounced", rather grew and shrank in size rapidly, meaning the voltage was varying wildly coming out of the 624.

I would also like to quote a site I found during Googling (and upload all images to Imgur) for longevity purposes and helping others incase that site goes down in a few years, as in addition to Tendril's post, it was a big help in not only knowing what chips to replace but WHY.

There are a few images pasted on the bottom of just the overall PCBs, which aren't really necessarily for the repair, and they were too large to upload to Imgur, so they've been excluded from the quote.

Original source: http://www.bryanmcphail.com/wp/?p=1917

BryanMcPhail.com said:
Sega Turbo is quite a complex pcb, certainly very complex for 1981, and also a bit of pain to repair. The video output isn't compatible with my usual Sony PVM test monitor (hence the red only display), but also it requires -12V as well as +12V which not all modern PSUs supply. The problem with this board is stretched sprites – in fact all sprites are stretched to their maximum value.

uixwEdE.png


The way the sprite scaling works is quite interesting – unlike the digital processing in most arcade games, the scaling is effectively analog. The clock signal used to read the sprite data can be sped up or slowed down with respect to the scanline pixel clock. So if the sprite clock is slower then the sprite will effectively be scaled bigger across the scanline as the sprite pixels 'smear' across multiple scanline pixels.

ltbDIT1.png


The current scale value is held in the LS373 at IC1 on the video board – the drives a digital to analog convertor – UPC624D which then drives a UPC159. Notice how the two analog components require -12V – without that the sprite clock will not run at all and there will be no sprites on screen. If the LS373 fails with all outputs high the board will display the maximum scale, likewise if the UPC624D fails with high output you get the same effect as both cases lead to the UPC159 getting maximum voltage. On this board the UPC624D had failed and was replaced to fix the problem.

41G5J6k.png
 
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So i think im having same issue except only thing stretched are the cars . Any suggestions? Tried the 2 pots but nothing. Thanks
 
Another thing interesting I discovered about this game is the way the roms work, you can remove image roms and it'll remove specific buildings trees or cars. So if you have a problem with a certain car, you can remove roms until you figure out which one does that car, then check the chips in the schematics on that level.
 
Another thing interesting I discovered about this game is the way the roms work, you can remove image roms and it'll remove specific buildings trees or cars. So if you have a problem with a certain car, you can remove roms until you figure out which one does that car, then check the chips in the schematics on that level.
I will check that out. I did clean all chips an reseated the chips. Thanks
 
Whoa neat! Thanks for posting, guys. Good that someone is figuring out how these work. I have a "spare" set that has some stuff wrong but still haven't gotten around to looking at it.
 
Whoa neat! Thanks for posting, guys. Good that someone is figuring out how these work. I have a "spare" set that has some stuff wrong but still haven't gotten around to looking at it.
Yes i replaced the l373 chip cause i found 1 that didnt fix but i have the upc624c chip coming
 
Well after replacing both those chips still have stretched cars. I have a seconds board set i just cleaned up reseated chips graphics decent but it to has stretched out graphics. Any other suggestions thanks
 
So to follow up. Got it solved with big cars. The little regulator board has a crack through it. All tested good but when i tapped on capacitor whammo cars went normal size graphics perfect.
 
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